Title: Deborah Estrin
1An Architecture for Sensor Networks Directed
Diffusion
- Deborah Estrin
- USC CS Dept and ISI
- In collaboration with
- Co-PIs Ramesh Govindan, John Heidemann
- Diffusion Chalermak Intanagowat, Amit Kumar
- Localized algorithms Jeremy Elson,Satish Kumar,
Ya Xu, Jerry
Zhao - Localization Lew Girod, Nirupama Bulusu
- Distributed robotics Maja Mataric, Gaurav
Sukhatme, Alberto Cerpa - For more information estrin_at_isi.edu
2The long term goal
Embed numerous distributed devices to monitor and
interact with physical world in work-spaces,
hospitals, homes, vehicles, and the environment
(water, soil, air)
Network these devices so that they can coordinate
to perform higher-level tasks. Requires robust
distributed systems of tens of thousands of
devices.
3Overview of research
- Sensor network challenges
- One approach Directed diffusion
- Basic algorithm
- Initial simulation results (Intanagowat)
- Other interesting localized algorithms in
progress - Aggregation (Kumar)
- Adaptive fidelty (Xu)
- Address free architecture, Time synch (Elson)
- Localization (Bulusu, Girod)
- Self-configuration using robotic nodes (Bulusu,
Cerpa) - Instrumentation and debugging (Jerry Zhao)
4The Challenge is Dynamics!
- The physical world is dynamic
- Dynamic operating conditions
- Dynamic availability of resources
- particularly energy!
- Dynamic tasks
- Devices must adapt automatically to the
environment - Too many devices for manual configuration
- Environmental conditions are unpredictable
- Unattended and un-tethered operation is key to
many applications
5Approach
- Energy is the bottleneck resource
- And communication is a major consumer--avoid
communication over long distances - Pre-configuration and global knowledge are not
applicable - Achieve desired global behavior through localized
interactions - Empirically adapt to observed environment
- Leverage points
- Small-form-factor nodes, densely distributed to
achieve Physical locality to sensed phenomena - Application-specific, data-centric networks
- Data processing/aggregation inside the network
6Directed Diffusion Concepts
- Application-aware communication primitives
- expressed in terms of named data (not in terms of
the nodes generating or requesting data) - Consumer of data initiates interest in data with
certain attributes - Nodes diffuse the interest towards producers via
a sequence of local interactions - This process sets up gradients in the network
which channel the delivery of data - Reinforcement and negative reinforcement used to
converge to efficient distribution - Intermediate nodes opportunistically fuse
interests, aggregate, correlate or cache data
7Illustrating Directed Diffusion
Setting up gradients
Source
Sink
8Local Behavior Choices
- 1. For propagating interests
- In our example, flood
- More sophisticated behaviors possible e.g. based
on cached information, GPS - 2. For setting up gradients
- Highest gradient towards neighbor from whom we
first heard interest - Others possible towards neighbor with highest
energy
- 3. For data transmission
- Different local rules can result in single path
delivery, striped multi-path delivery, single
source to multiple sinks and so on. - 4. For reinforcement
- reinforce one path, or part thereof, based on
observed losses, delay variances etc. - other variants inhibit certain paths because
resource levels are low
9Initial simulation studies(Intanago, Estrin,
Govindan)
FLOODING
- Compare diffusion to a)flooding, and b)centrally
computed tree (ideal) - Key metrics
- total energy consumed per packet delivered
(indication of network life time) - average pkt delay
DIFFUSION
CENTRALIZED
CENTRALIZED
DIFFUSION
FLOODING
10What we really learnt (things we dont usually
showbecause in retrospect they seem so obvious)
- IDLE time dominates energy consumptionneed low
duty cycle MAC, driven by application. - With 802.11ish contention protocols you might as
well just FLOOD - Easy to get lost in detailed simulations but in
the wrong region of operation - Node density, traffic load, stream length, source
and sink placement, mobility, etc.
11Exploring Diffusion
- Aggregation
- Adaptive Fidelity
- Implications
- address free architecture
- Need for localization
- Using diffusion
- System health measurements
- Robotic nodes
12Diffusion based Aggregation(Kumar, Kumar,
Estrin, Heidemann)
- Scaling requires processing of data INSIDE the
net - Clustering approach
- Elect cluster head (various promotion criteria)
- Aggregation or Hashing (indirection) to map from
query to cluster head - Opportunistic aggregation
- Reinforce (request gradient) proportional to
aggregatability of incoming data (Amit Kumar)
13Adaptive Fidelity(Xu, Estrin, Heidemann)
- In densely deployed sensor nets, reduce duty
cycle engage more nodes when there is activity
of interest to get higher fidelity - Adjust node's sleeping time according to the
number of its neighbors. - Initial simulations applied to ad hoc routing
- Performance Metric Percentage of survived nodes
over time. - The more nodes survive, the longer network
lifetime
14Comparison Density factor
- At the left, from top to the bottom Adaptive
Fidelity, Basic algorithm, regular AODV - Simulation under 50 nodes, 100 nodes, 150 nodes
- Network lifetime is extended by deploying more
nodes only with adaptive fidelity algorithm - Simulations available (ns-2 based)
15Comparison Traffic Factor
- At the left, from top to the bottom Adaptive
Fidelity, Basic algorithm, regular AODV - Simulation under different traffic load 5pkt/s,
10pkt/s, 15pkt/s, 20pkt/s - Longer network lifetime in adaptive
- The more traffic load, the greater the advantage
in terms of network lifetime
16Adaptive Fidelity conclusions
- Must be applied at application level (because
just listening/having radio on dominates energy
dissipation) - Unfortunate side effect of resource constraints
is the need to give up (some) layering - Many open questions as to density thresholds and
how to design algorithms to exploit it.
17Implications local addresses?
- Sensor nets maximize usefulness of every bit
- each bit transmitted reduces net lifetime
- cant amortize large headers for low data rates
- underutilized address space is bad
- Still need to identify transmitter
- Reinforcements, Fragmentation
- Use small, random transaction identifiers
(locally selectedlike multicast addresses) - Treat identifier collisions as any other loss
- Address-free method can win in networks with
locality - simultaneous transactions at any one point is
much less than in network as a whole
18- No need for global address assignmentbut how
inefficient is it? - AFA optimizes number of bits used per packet
- o Fewer bits less overhead per data bit
- o More bits less contention loss
Efficiency of AFA as a function of local address
size.
19Implcations Need Localization(Bulusu, Girod)
- Many contexts you cant have GPS on every node
- form factor
- energy
- obstructions
- Beacon architecture
- Signal strength alone problematic/hopeless
- Federated coordinate systems
- Acoustic ranging (client node asks beacons to
send chirp and monitors time of flight) - Self-configuring beacon placement using robotic
nodes
20Localization is a critical service(Girod)
- Devices take up physical space
- Sufficiently fine-grained spatial coordinates
provide implicit routing information (e.g.
directing interests) - Location is relevant to many applications
- Devices are doing things in the world users need
to find them inputs and outputs to tasks often
reference locations - How can we achieve fine-grained localization?
- Need sensors to measure distance (ranging)
- Time arrivals of 3 requested acoustic signals
not signal strength - Relative or Global?
- Relative spatial measurements more accurate
because observed phenomena are local, shorter
ranges, etc. - Global measurements (e.g. GPS) coarser (40m) but
provide single coordinate system that can be
exported unambiguously - Combine global scope of GPS with precision of
relative sensors fuse local global coordinate
frames
21Localization relies on beacons(Bulusu,
Heidemann, Estrin)
- Precision of localization depends on beacon
density/placement - Uniform placement not good solution in real
environments - Obstacles, walls, etc prevent inference based on
signal strength/proximity detection - Self-configuring beacon placement is interesting
application for robotic nodes - Given obstacles, unpredictable propagation
effects, need empirical placement
22Sensor Network Tomography(Zhao, Govindan, Estrin)
- Continuously updated indication of sensor network
health - Useful for
- performance tuning
- adjusting sensing thresholds
- incremental deployment
- refurbishing sections of sensor field with
additional resources - self testing
- validating sensor field response to known input
Tomogram indicating connection quality
23Sensor Network Tomography Key Ideas and
Challenges
- Kinds of tomograms
- network health
- resource-level indicators
- responses to external stimuli
- Can exchange resource health
- during low-level housekeeping functions
- such as radio synchronization
- Key challenge energy-efficiency
- need to aggregate local representations
- algorithms must auto-scale
- outlier indicators are different
24Self configuring networks using and supporting
robotic nodes(Bulusu, Cerpa, Estrin, Heidemann,
Mataric, Sukhatme)
- Robotics introduces self-mobile nodes and
adaptively placed nodes - Self configuring ad hoc networks in the context
of unpredictable RF environment
- Place nodes for network augmentation or formation
- Place beacons for localization granularity
25CONCLUSIONS
- Have just scratched the surface
- We need to put more experimental systems in place
and start living in instrumented environments or
we risk too many rat-holes and pipe-dreams - Long-term and High-impact opportunities
- Biological monitoring
- Environmental sensing
- Medical applications based on micro and nano
scale devices - In-situ networks for remote exploration